Method of making multifocal lens segments



April 2, 1935..

'N. Mi STANLEY METHOD OF MAKING MULTIFOCAL LENS 'SEGMENTS 2 Shee'ts- Sheet l Filed A 24, 1933 V Tuar bo 4 NATHAN M.5 AN EV, E

mama@ April 2, 1935. N. M. STANLEY 1,996,442

.METHOD OF MAKING MULTIFOCAL LENS SEGMENTS Filed April 24,`1955 2 Sheets-Sheet 2 NATHAN M.sTA'N E-Y,

atent Apr. 2, 1935.

G m'rmocaa seems METEO!) OF m Nathan M. Stanley, Dayton, Ohio. -assignor to The Univis Corporation, Dayton, Dhima corporation of Delaware ApplicationApril 24, 1933, Serial No. sensit 4 Claims. (ci. 49421 This invention relates to multifocal lenses and, in particular, to segments for multifocallenses and methods of making them.

One object of my invention is to provide a method of making a `multiocal lens segment of the sp-called compound button type wherein the necessity of flnishing the adjoining edges or of clamping them' together, is eliminated.

Another' object is to provide a method of making such a segment which shall be inexpensive, simple and emcient, and which will result in an improved product well adapted to manufacture by quantity production methods.

Another object is"to,p`rovide a method-of making such a segment wherein the junction between two adjoining parts will have a light-retarding layer therebetween to prevent the reflection oi' light from the inter-edge between the parts having different indices oi refraction, or to prevent the production of color fringes near said inter-edge.

Another object is to provide such allight-retarding 'layer which will be translucent rather than completely transparent :or completely opaque.

Another object is to provide such a light-retarding layer which is of a different chemical composition from that of the other parts of the segment.

Another object is to provide a method of making such a segment wherein the light-retarding layer will be produced by Chemical attack on one or more of the segment parts.

Other objects will be apparent from the following specication taken in connection with the accompanying drawings and appended cla'ms.

In the drawings:

Figure 1' is a plan view of one part, preferably low index glass, used in making the segment of my invention.

Figure 2 is a plan view of another part, preferably of high indexglass, used in making such a segment.

Figure 3 is a perspective view showing a roughened edge formed on one of the segment parts.

Figure 4 is a bottom view of the lower surface of one of the segment parts, showing the roughened treatment which may be given thereto in 'order that the inter-edge between the segment Figure '1 is a view similar to Figure 5 with the fusing completed.

Figures is a plan view of the segment or button after fusing, as shown in Figure 7. Figure 9 is a side elevation of the complete segment shown in rough form in Figure 8 after surfacing. 5

Figure 10 is a side elevation of a completed segment similar to that shown in Figure 8, but with a light-diffusing layer between the segment' parts.

Figure 'll is a plan view of a major blank showing 'a countersink for re'ceiving a segment.

Figure 12 .is a central-vertical section through the major blank shown in Figure 11.

Figure 13 is a plan view`- of the major blank shown in Figure 11, in position on a fusing block,

with the segment or button shown in Figure 8 held in position over the countersink.

the segment fused into the counter- 16 after the segment side has been ground and polished, showing the `outline of a finished lens in dotted lines.

Figure 18 is a central vertical section through a fusing block containing a modified arrangement of segment parts.

Referring to the drawings in detail, i is a piece of transparent material for a segment, preferably of low index crown glass.' `(Figure 1). 2 is' a corresponding. segment piece of high index `glass, preferably of flint or barium crown glass. (Figure 2). In carrying'out my invention, it is preferable to roughen the' edge &of the crown piece l to prevent light reflections at the interedge between the' segment portions, as the. low index piece usually has a. higher melting point than the high index piece 2. It is also advisable,

although not entirely necessary, to roughen 'the bottom surface& of the high index portion 2, as shown in Figure 4.

The pieces thus prepared are assembled in the I manner shown in Figure 5, using a heat resisting holder 5, 'this holder or fusing block being of. any suitable material which will en'dure the high temperatures without` disintegration or warping. Carborundum has been found suitable, also porcelain, fire clay and certaimmetals. The fusing block 5 preferably contains a recess G or projections 'I and 8 which serve to keep the segment parts from slipping. The low index, portion is placed against one of these projections or side walls 8 and the high index portion is tilted with one edge supported against the other projection or side wall 1, the opposite edge being supported. as at 9, on the upper edge of the low index por.- tion i. The overlap at 9 of the high index portion 2 upon the low index portion i may be very small, an overlap of one or two millimeters usually being ample. If the surface I of the hish index portion has been uniformly roughened, as in Figur-e 4, it is placed downward toward the fusing block, as in Figure 5. r

With the segment paris in the position shown in'Figure 5, the assembly is placed in a suitable furnace, and the temperature raised to the fusing point. The furnace may be of the stationary type wherein the fusing block remains in one position throughout the entire fusing operation; ,or it may be of the movable typewherein the fusing block and its contents move gradually through the fumace under the influence of conveying mechanism.

When the temperature reaches the softening point of the high index glass. assumed to be also the lower melting glass, the latter begins to collapse as shown in Figur-e '6. During this stage of the method, the low melting portion 2 first s-' sumes the shape of `the letter I, -then coilapses into the form of a letter J, andflnally the form somewhat like a letter L with its'stubbed lower bar pointed upward, as shown in, Figure TI. Under the action of the heat, the stubbed bar disappears in a rounded ridge "which passes 'across the segment, following the direction of the inter-edge 3. Accordingly, as the low melting ;part 2 collapses (Figure 6), the portion Il-,-|2

thereof comes into contact with the edge 3 of the higher melting portion, whereas the end I: finally -assumes a substantially horizontal position and becomes the rounded ridge II.

The temperature' necessary to produce this welding of the button parts depends entirely on the particular materials used; For the average fiint glass portion superposed on a crown glass portion, about 65o c. or 2oo r'. is a average temperature. For a barium crown segment portion on a crown segment portion, however. the temperature must be raised considerably, and

about 750 C. or 1380" F. is suitable for one kind' of this glass. Du'ing the fusion, it is advisable to dust the fusing block with powdered mica or an analogous material in order to prevent the;

button parts from sticking to the fusing block. After fusion` has taken place, the heat is turned oi! and the button allowed to anneal in a closed furnace for a period. of ten hours. or more. as

conditions demand, in order that all strain will be eliminated. In a furnace of the moving type,

the button parts will pass through the annealing stage in a period several" hours shorter in length. The rough button thus made is now surfaced on both sides. 'One surface M has acurvature suitable for fusing into a countersink li in a major' blank !6 (Figure 11) this major blank beingpreferably of low index material. The other side l'l of the button may be left. roughor preferably finished with a suitable curve which will allow the segment to be inspected for dei'ects by looking through it. The' curvature of the countersink IS- in the major blank IS is determiied by the particular reading addition which it is desired to create on. the given base curve ll' (Figu'e 12% This curvatre is readily determined by-formulae wellknowntojhoseskilledinthe art. Theopposite side I! of the major blank II is given a surface whose curvature corresponds to the curvature on the upper surface 20 of a second fusing` s block !I (Figure 14). It is important that the .cui-ves I! and 2! be very closely in correspondence, otherwise the-blank IS may warp silently causing a distortion of the countersink and a consequent damage to the optical quality 'o of the lena. The second fusing block may be made of the same material as the first fusing block. The segment may be held in position over the eountersink II'bya clip 22 and by guiding spote' 23. (Figur-e 13). The clip 22 may beof s the segment slightly tilted or separated from the countersink !5 bg 811,', space of *varying Whith.` z: The result is that when the assembly is placed in a stationary .or moving furnace and the temperature raised to the fusing point, the segment slowly collapses-and becomes joined to the countersink ls driving the air out ahead of it as it 34 collapm into' the countersink li. .As before. the proper fusing temperature depends ou the materials used, a temperature of about 700 C.

-or 1290" F. being suitable for flint glass and about 750 C. or 1380" F. for barium crown glass. It 3` is, of course, assumed that the contacting surfaces M of the button, and li of the countersink have been cleaned in a suitable manner prior to fusing, 'such as by using alcohol. weak acids or alkalies. The blank thus made is annealed for 4 atime andin amanner similar to the annealing period for the segment fusion previously descrihed. Prior to fusion, the surface 20 of the fusing block 2] is preferably dusted with powdered mica oiother; similar substanca to' prevent; sticking The rough blank thus formed (Figure 16) is now surfaced on its segment side '24 with the curvature of the particular base curve s chosen 'to give the desired addition. The semi-finished e blank thus formed is sold in that form to the optician who makes it into a finished lens by surfacig the opposite sidewith a curvature suitable for the individual prescription of the wearer,

The flnishedlens of a suitable size and-shape is I then cut out, as shown by the dotted "linos 25 in i Figur-e 17, and. after being edge-ground, is mounted in the ordinary manner .well known in etheart; Y o The inter-edge, or the edge along which the two portions I and 2 are joined, may be treated in any one of several diiferent ways, but variously treating the edge I, of the high melting portion and the surface H-l2 of the low melting portion (figure 6) according as whether or not it is i desired to remove reflections along this interedge; If such reflections are not to be eliminated, the edge 3 may be ground and polish d and the bottom surface 4 of the low melting portion likewise ground and polished, A partial reduction of the inter-edge reflections will be obtained if the edge 3 is ground but not polished, and this eifect will be increasedif the bottom surface 4, or at least the portion ll-l2 thereof, be also ground but not Under this treatment the in- Alternatively, pieces of cardboard sc -tioas to' mite completely. As an example of such .reflection prevention is -desired, I have found several means of accomplishing this purpose.

g By one modification of my invention, I find that a light-retarding layer may be inserted along the inter-edge by coating the edge 3 and/orthe portion i |,-|2 of the surface 4 with a substanca `'Patent is:

1. A method of making a multifocal lens s ment, including supporting one end of one seg- -which willsuflicientlyresist the action of the iusing beat-to create a diflfusion of the light rays which would otherwise be 'reflected oiI` the inter-edge. such sub ce must likewise be -of such a character that it will accbmplish this light difrusion and yet permit the segment .por-

a substance which will permiti'usion and yet V *produce such a light-dlflusing layer, I ilnd that an 'ordinary red lead pencil may be rubbed over the areas tobe joined prior to fusion: -the unpolished condition ofthese areas permits the adhesion of the pencil material more readily than than the adjacent glasses, as distinif these areas were polished. such pencils are composed p'rincipally of a wax in which red lead (Pbaoi) is dissolved to provide the red pigment. When the glasses are-raised to the high 'temperamre of fusing; the redlead breaks down into lead monoxide (PbO) which is of a pale yellowish i white color and which provides the light difnsing layer. It isimportant not to use too waxy' a pencil, as an excess of stearin may' 'prevent proper fusion and 'cohesion of the parts. I e

It is not intended to limit the invention to this single'substance, as it is found that many substances which will endure the high heat of fusion provide a similar light-diil'using layer.: The

layer thus produced is of difierent chemical comguished'from a light-producing inter-edge form ed by leaving the contacting edges ground but not before usionz-the ground surface of 'the the'highenmeltingportion maybe given an arcuate Outline and the 'beneflts of my invention equally aflorded. In producing such a segment with an. arcuate inter-edge. the projecting ridge o will obviously become arcuate in shape rather than a straight rldge across the surface of the segmentasshowninl 'igures.`

g It will beiunderstood that I desire to comprehend within my invention such modiflcations as may be necessary to adapt it to varying conditions- Having thus fully described my invention, what I claim'as new and desire to secure by Letters ment portion upon the upper comer of another segment portion, and applying heat to cause said upper portion to buckle and become united with said lower segment portion along an edge only thereof.

2. A method of making a multifocal lens segment, including providing one segment portion with a roughened bottom surface, partially superposing this portion upon another segment portion with said roughened surface downward, and

appiying suiiicient heat to cause said upper'portion to' buckle and become united to said lower segment portion along an edge thereof. I

3. VA method of making a multifocal lens segment, including placing one segment portion on a refractory support, applying a coating of lightdiifusing material to one surface of another segment. portion. -superposing said second segment portion in slightly overlappingrelationship upon said 'first segment portion, andapp y s heat to cause said portions to become i'oined along edge of one of said portions with said lightdiifusing ayer between said portions so-ioined.

4. A method of making a multii'ocal lens segment, including placing a higher mclting segment portion on a refractory support, applying a coat.-

ing of light-diilusing material to one surface of a lower' melting segment portion, superposing said lower melting portion upon 'said higher melt'- ing portion in slightly overlappin'g relationship, and pp yi s heat to cause said portions to be.- come `joined along an edge of one of said portions withsaid light layer between said portions so-Joined.

' NATHAN IM. STANLEY. 

